Spurious mode suppression in bulk acoustic wave resonator

ABSTRACT

Embodiments provide a solidly-mounted bulk acoustic wave (BAW) resonator and method of making same. In embodiments, the BAW resonator may include a planarization portion in an inactive region of the BAW resonator that is coplanar with a piezoelectric layer of the BAW resonator in an active region of the BAW resonator. Other embodiments may be described and claimed.

RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 14/711,679, filed May 13, 2015, now U.S. Pat. No. 9,985,194,entitled “SPURIOUS MODE SUPPRESSION IN BULK ACOUSTIC WAVE RESONATOR,”the disclosure of which is hereby incorporated herein by reference inits entirety.

FIELD

Embodiments of the present disclosure relate generally to the field ofresonators, and more particularly to spurious mode resonance suppressionin bulk acoustic wave (BAW) resonators.

BACKGROUND

Lateral acoustic waves, also referred to as Lamb waves, may propagatethrough portions of an active region of a bulk acoustic wave resonatordue to finite lateral dimensions of the BAW resonator structure. Thismay result in part of the energy contained in a fundamental thicknessmode (i.e., a vertically resonating mode) leaking to lateral modes(i.e., a horizontally resonating mode), which results in a degradationof a quality factor of the BAW resonator. Lateral acoustic waves maybecome evident in electrical behavior of the BAW resonator in the formof spurious resonances leading to strong ripples in the bandpassfrequencies.

Performance of a BAW resonator may be improved by creating a region withspecific boundary conditions in which lateral acoustic waves cannotpropagate. For some resonators, this may be done by including athickened edge load, known as a border ring (BO), in a perimeter of anactive region of the BAW resonator. Presence of the thickened edgeenables the mismatch between the active and inactive regions to beavoided, providing a smooth transition of propagating waves in theactive region to evanescent waves in the inactive region.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments are illustrated by way of example and not by way oflimitation in the figures of the accompanying drawings, in which likereferences indicate similar elements.

FIG. 1 illustrates a BAW resonator in accordance with some embodiments.

FIG. 2 is a graph illustrating BAW resonator performance in accordancewith some embodiments.

FIG. 3 illustrates a graph illustrating BAW resonator performance inaccordance with some embodiments.

FIG. 4 illustrates a graph illustrating BAW resonator performance inaccordance with some embodiments.

FIG. 5 is a flowchart depicting a manufacturing operation of a BAWresonator in accordance with some embodiments.

FIG. 6 illustrates a wireless communication device in accordance withsome embodiments.

DETAILED DESCRIPTION

Various aspects of the illustrative embodiments will be described usingterms commonly employed by those skilled in the art to convey thesubstance of their work to others skilled in the art. However, it willbe apparent to those skilled in the art that alternate embodiments maybe practiced with only some of the described aspects. For purposes ofexplanation, specific devices and configurations are set forth in orderto provide a thorough understanding of the illustrative embodiments.However, it will be apparent to one skilled in the art that alternateembodiments may be practiced without the specific details. In otherinstances, well-known features are omitted or simplified in order not toobscure the illustrative embodiments.

Further, various operations will be described as multiple discreteoperations, in turn, in a manner that is most helpful in understandingthe present disclosure; however, the order of description should not beconstrued as to imply that these operations are necessarily orderdependent. In particular, these operations need not be performed in theorder of presentation.

The phrase “in one embodiment” is used repeatedly. The phrase generallydoes not refer to the same embodiment; however, it may. The termscomprising, having, and including are synonymous, unless the contextdictates otherwise.

The phrase “coupled with,” along with its derivatives, may be usedherein. Coupled may mean that two or more elements are in directphysical or electrical contact. However, coupled may also mean that twoor more elements indirectly contact each other, but yet still cooperateor interact with each other, and may mean that one or more otherelements are coupled or connected between the elements that are said tobe coupled with each other.

In various embodiments, the phrase “a first layer formed on a secondlayer” may mean that the first layer is formed, disposed, or otherwiseconfigured over the second layer, and at least a part of the first layermay be in direct contact (e.g., direct physical and/or electricalcontact) or indirect contact (e.g., having one or more other layersbetween the first layer and the second layer) with at least a part ofthe second layer.

As described above, in some cases a BAW resonator may include an activeregion designed to resonate according to a fundamental thickness mode,which may be considered to be vertically or along a z-axis of the BAWresonator. However, in some cases the energy contained in thefundamental thickness mode may propagate through the BAW resonator aslateral acoustic waves, that is, horizontally/laterally/along anx/y-axis of the BAW resonator. This leakage may result in degradation ofthe quality factor of the BAW resonator. Specifically, in some caseslateral standing waves may become evident in the electrical behavior ofthe BAW resonator in the form of spurious resonances that may lead tostrong ripples in bandpass frequencies of the BAW resonator.

In some cases, the performance of the BAW resonator can be improved byintroducing a border ring or border region at the perimeter of theactive region of the BAW resonator. In some cases the border region maybe introduced by adding mass to a portion of the BAW resonator asdescribed below. Alternatively, in some cases the border region may beintroduced by removing mass from one or more layers of the BAW resonatorwithin the border region, as described below. Generally, the borderregion may separate the active region of the BAW resonator from aninactive region of the BAW resonator. The border region may enable themismatch between the active region and the inactive region to beavoided, providing a smooth transition of propagating waves in theactive region to evanescent waves in the inactive region, therebyreducing spurious mode resonances of the BAW resonator. To do so, thelateral propagation constant k_(x) in the active region may ideally be areal constant, while it may ideally be purely imaginary in the inactiveregion.

In some embodiments, a BAW resonator may show decreased amounts ofspurious mode resonances in bandpass frequencies, but there may still besome amount of spurious mode resonance. Embodiments herein relate to BAWresonators with even further decrease of spurious mode resonances.

FIG. 1 depicts an example of a first embodiment of a BAW resonator 100with reduced spurious mode resonance, in accordance with variousembodiments. The BAW resonator 100 may be, for example, a solidlymounted BAW resonator. Elements of the BAW resonator 100 may bedescribed with respect to a vertical axis and a horizontal axis asdepicted in FIG. 1. In some embodiments, the BAW resonator 100 mayinclude an axis of symmetry that is a generally vertical axis withrespect to FIG. 1, and depicted by the line of alternating dots anddashes.

In some embodiments, the BAW resonator 100 may include planarization ofa piezoelectric layer of the BAW resonator 100 with a planarizationmaterial in the inactive region, as described in further detail below.By planarizing the piezoelectric layer of the BAW resonator 100 with theplanarization material, the inactive region cut-off frequency of the BAWresonator 100 may move relative to the position of the resonancefrequency of the active region. The change in mechanical characteristicsof the inactive region may change the decay rate of evanescent wavesresulting in a smoother transition of propagating waves in the activeregion to evanescent waves in the inactive region. In a legacy BAWresonator, the piezoelectric layer 116 may be extended all the way intothe inactive region covering the planarization portion 124.

The BAW resonator 100 may include an active region 104, a border region108, and an inactive region 112. Generally, the active region 104 may bea part of the BAW resonator 100 that is electrically driven, and includea piezoelectric layer 116 sandwiched between a top electrode 105 and abottom electrode 132. Specifically, the top electrode 105 and the bottomelectrode 132 may drive resonance of the piezoelectric layer 116 withinthe active region 104 according to the fundamental thickness modedescribed above. The active region 104 may further include a mirrorlayer 144 that may also be referred to as a Bragg mirror layer in someembodiments. The active region 104 may further include a substrate layer107.

The border region 108 may additionally include the top electrode 105,the piezoelectric layer 116, the bottom electrode 132, the mirror layer144, and the substrate layer 107. In some embodiments the border region108 may optionally include a mass 115 that may increase the overall massof the BAW resonator 100 within the border region 108. In otherembodiments, the border region 108 may include a portion of the topelectrode 105, the piezoelectric layer 116, the bottom electrode 132,and/or the mirror layer 144 with reduced mass. Whether the mass isincreased or decreased in the border region 108 may be based, forexample, on the resonator dispersion type, on specific applications withwhich the BAW resonator 100 may be used, or one or more other factors.In general, a BAW resonator can have type I or type II dispersion,referring to the position of a longitudinal main resonance mode (TE1)and a second shear resonance mode (TS2) in the frequency domain.Generally, if the frequency at which TE1 occurs is greater than thefrequency at which TS2 occurs, then the dispersion may be referred to astype I dispersion. If the frequency at which TS2 occurs is greater thanthe frequency at which TE1 occurs, the dispersion may be referred to astype II dispersion. Generally, the border region 108 is depicted in FIG.1 to vertically extend through the BAW resonator 100 within the verticaldashed lines of FIG. 1.

The inactive region 112 may be the part of the BAW resonator 100 that isnot electrically driven, for example, by the top electrode 105 and thebottom electrode 132. The inactive region 112 may include the substratelayer 107 and the mirror layer 144. The inactive region 112 may furtherinclude a planarization portion 124 that is generally coplanar with atleast the piezoelectric layer 116 as indicated by the horizontal dashedlines in FIG. 1. That is, the planarization portion 124 may be laterallyor horizontally next to the piezoelectric layer 116. In embodiments, thematerial of the planarization portion 124 is different from that of thepiezoelectric layer 116 and it may be formed of a material that may besimilar to a material of the mirror layer 144.

In some embodiments, the mass 115 may be formed of or include adielectric material, a material similar to that used in the topelectrode 105, and/or some other material.

In some embodiments, the top electrode 105 and/or the bottom electrode132 may include one or more layers. For example, as depicted in FIG. 1,the top electrode 105 and the bottom electrode 132 include a first layer136 and a second layer 140. The first layer 136 may be directly coupledwith the piezoelectric layer 116, and the second layer 140 may be alayer of the electrode that is not directly next to the piezoelectriclayer. In some embodiments the top electrode 105 and/or the bottomelectrode 132 may include only a single layer, or three or more layers.The first layer 136 may include a material such as Tungsten (W). Thesecond layer 140 may include a material such as an Aluminum Copper(AlCu) compound. Other materials may be used in other embodiments.

The piezoelectric layer 116 may include a piezoelectric material such asAluminum Nitride (AlN) or some other piezoelectric material. Thesubstrate layer 107 may include a dielectric material such as Silicon(Si) or some other suitable substrate material.

The mirror layer 144 may include alternating layers of a dielectricmaterial 148, for example, Silicon Oxide (SiO₂), and a conductivematerial 152, for example, Tungsten (W). As shown in FIG. 1, thedielectric material of the reflector layer(s) 148 may be the samematerial as that used in the planarization portion 124. In otherembodiments, a different material may be used between one or more of thereflector layer(s) 148 and/or the planarization portion 124.

As shown in FIG. 1, in some embodiments one or more of the conductivematerial layer(s) 152 may extend farther into the inactive region 112than another of the conductive material layer(s) 152. For example, asdepicted the bottom conductive material layer 152 (as viewed withreference to FIG. 1) may extend farther than the top conductive materiallayer 152 (as viewed with reference to FIG. 1). For example, the bottomconductive material layer 152 may extend farther than the top conductivematerial layer by 3 to 5 microns. Although three of the dielectricmaterial layers 148 and two of the conductive material layers 152 aredepicted in FIG. 1, in other embodiments a higher or lower number ofdielectric material layer(s) 148 and conductive material layer(s) 152may be used in the BAW resonator 100. Also, the thicknesses depicted inFIG. 1 are intended to be examples of one embodiment, and otherembodiments of the BAW resonator 100 may have different thicknesses ofthe different layers and/or elements.

In some embodiments, the planarization portion 124 may further smooththe transition of the lateral propagation constant k_(x) in the activeregion 104 from a real constant to an imaginary constant in the inactiveregion 112. By smoothing this transition, the spurious mode resonancesof the BAW resonator 100 may be further reduced.

FIG. 2 depicts an example of spurious mode suppression that may beachieved by planarization of the piezoelectric layer 116 with theplanarization portion 124 in the inactive region 112. Specifically, FIG.2 depicts an example of impedance phase of a BAW resonator such as BAWresonator 100 operating with a type I dispersion curve. FIG. 2 depictsan example that includes both a graphic illustrating both the bandpassportion 205 of the BAW resonator as well as a region 210 adjacent to thebandpass portion 205. FIG. 2 further depicts detailed graphics of thebandpass portion 205 and the region 210 adjacent the bandpass portion205. The dashed line indicates a legacy BAW resonator operating withouta border region 108. The dotted line indicates a legacy BAW resonatoroperating with a border region 108. The solid line indicates a BAWresonator such as BAW resonator 100 operating with both a border region108 and a planarization portion 124. As can be seen in FIG. 2, theperformance of the BAW resonator 100 in the bandpass region 205 may besignificantly smoother than the performance of either of the legacy BAWresonators. Additionally, the performance of the BAW resonator 100 in aregion 210 adjacent to the bandpass region 205 may also be significantlysmoother than the performance of either of the legacy BAW resonators. Asdepicted in FIG. 2, the material in the piezoelectric layer 116 may beAlN (in all three cases) while the planarization material in theplanarization portion 124 may be SiO₂.

FIG. 3 depicts an example of spurious mode suppression that may beachieved by planarization of the piezoelectric layer 116 with theplanarization portion 124 in the inactive region 112. Specifically, FIG.3 depicts an example of impedance phase of a BAW resonator such as BAWresonator 100 operating with a type II dispersion curve. FIG. 3 depictsan example that includes both a graphic illustrating both the bandpassportion 305 of the BAW resonator as well as a region 310 adjacent to thebandpass portion 305. FIG. 3 further depicts detailed graphics of thebandpass portion 305 and the region 310 adjacent the bandpass portion305. The dashed line indicates a legacy BAW resonator operating withouta border region 108. The dotted line indicates a legacy BAW resonatoroperating with a border region 108. The solid line indicates a BAWresonator such as BAW resonator 100 operating with both a border region108 and a planarization portion 124. As can be seen in FIG. 3, theperformance of the BAW resonator 100 in the bandpass region 305 may besignificantly smoother than the performance of either of the legacy BAWresonators. Additionally, the performance of the BAW resonator 100 in aregion 310 adjacent to the bandpass region 305 may also be significantlysmoother than the performance of either of the legacy BAW resonators. Asdepicted in FIG. 3, the material in the piezoelectric layer 116 may beAlN (in all three cases) while the planarization material in theplanarization portion 124 may be SiO₂.

FIG. 4 depicts an example of spurious mode suppression that may beachieved by planarization of the piezoelectric layer 116 with theplanarization portion 124 in the inactive region 112. Specifically, FIG.4 depicts an example of impedance phase of a BAW resonator such as BAWresonator 100 operating with a type I dispersion curve. FIG. 4 depictsan example that includes both a graphic illustrating both the bandpassportion 405 of the BAW resonator as well as a region 410 adjacent to thebandpass portion 405. FIG. 4 further depicts detailed graphics of thebandpass portion 405 and the region 410 adjacent the bandpass portion405. The dashed line indicates a legacy BAW resonator operating withouta border region 108. The dotted line indicates a legacy BAW resonatoroperating with a border region 108. The solid line indicates a BAWresonator such as BAW resonator 100 operating with both a border region108 and a planarization portion 124 that includes a planarizationmaterial such as SiN. The line indicated by dash-dot indicates a BAWresonator such as BAW resonator 100 operating with both a border region108 and a planarization portion 124 that includes a planarizationmaterial such as HfO₂. As can be seen in FIG. 4, the performance of theBAW resonator 100 with the planarization portion 124 that includes aplanarization material such as SiN and/or HfO₂ in the bandpass region405 may be significantly smoother than the performance of either of thelegacy BAW resonators. Additionally, the performance of the BAWresonator 100 with the planarization portion 124 that includes aplanarization material such as SiN and/or HfO₂ in a region 410 adjacentto the bandpass region 405 may also be significantly smoother than theperformance of either of the legacy BAW resonators. The material in thepiezoelectric layer 116 may be AlN in all four cases.

FIG. 5 depicts an example process 500 for fabricating a BAW resonatorsuch as BAW resonator 100. Initially, a substrate layer may be depositedat 505. The substrate layer deposited at 505 may be similar, forexample, to substrate layer 107. Specifically, the substrate layer mayinclude a material such as Si.

The process 500 may include depositing a mirror layer such as mirrorlayer 144 at 510. The mirror layer deposited at 510 may include, forexample, one or more alternating layers of a conductive material layer152 and a dielectric material layer 148. In some embodiments, one ormore of the conductive material layer(s) 152 may extend partiallythrough an active region 104 and a border region 108 of the BAW 100, andinto an inactive region 112.

The process 500 may further include depositing a bottom electrode at515, for example, bottom electrode 132. In some embodiments the bottomelectrode may include a first layer 140 that may be a material such asan AlCu compound, and a second layer 136 that may be a material such asTungsten (W).

The process 500 may further include depositing a piezoelectric layersuch as piezoelectric layer 116 at 520. The piezoelectric layer mayinclude a piezoelectric material such as AlN.

The process 500 may further include depositing a top electrode at 525,for example, top electrode 105. The top electrode and bottom electrodemay include a first layer 136 that may be a material such as Tungsten(W), and a second layer 140 that may be a material such as an AlCucompound.

In some embodiments, the process 500 may optionally include depositing aplanarization portion at 530 such as planarization portion 124.

In some embodiments, the process 500 may optionally include depositing aborder region mass at 535 such as mass 115. In some embodiments, theprocess may not include depositing the border region mass at 535 becausethe border region 108 may have been defined by a portion of the topelectrode 105, piezoelectric layer 116, bottom electrode 132, and/ormirror layer 144 in the border region 108 that has reduced mass ascompared to a portion of the same layer in the active region 104.

The process 500 is intended as only an example of one process that maybe used to construct a BAW resonator such as BAW resonator 100. In otherembodiments, the BAW resonator 100 may be constructed via a differentprocess or manufacturing technique. For example, in some embodimentssome elements may be performed in a different sequence than depicted inprocess 500. As described herein, the deposition of different layers maybe performed via sputter deposition, lamination, or some other type ofdeposition or construction.

Although specific materials are discussed above with respect to someembodiments, in other embodiments different materials may be used. Forexample, the top electrode 105 and bottom electrode 132 are described asincluding Tungsten (W) and Aluminum-Copper (AlCu), however in otherembodiments additional and/or different materials may be used in the topelectrode 105 and/or bottom electrode 132. Similarly, although thepiezoelectric material of piezoelectric layer 116 is described asAluminum Nitride (AlN), in other embodiments the piezoelectric layer 116may include additional and/or different piezoelectric materials.Similarly, although the dielectric material of the substrate layer 107and/or the mirror layer 144 are described as Silicon (Si) and/or SiliconOxide (SiO₂), in other embodiments an additional and/or differentsuitable dielectric material may be used. Additionally, althoughTungsten (W) is described as the conductive material of the mirror layer144, in other embodiments additional and/or different conductivematerials may be used. Additionally, although the planarization portion124 is described as including Silicon Oxide (SiO₂), Silicon Nitride(SiN), and/or Hafnium Oxide (HfO₂), in other embodiments theplanarization portion 124 may include a different and/or additionalplanarization material.

A wireless communication device 600 is illustrated in FIG. 6 inaccordance with some embodiments. The wireless communication device 600may have an antenna structure 604, an antenna switch module (ASM) 608, afilter 612, a power amplifier (PA) 616, a transceiver 620, a processor624, and a memory 628 coupled with each other at least as shown.

The antenna structure 604 may include one or more antennas to transmitand receive radio frequency (RF) signals over the air. The antennastructure 604 may be coupled with the ASM 608 that operates toselectively couple the antenna structure with the filter 612 or the PA616. When receiving incoming RF signals, the ASM 608 may couple theantenna structure 604 with the filter 612. The filter 612 may includeone or more BAW resonators, such as BAW resonator 100. In someembodiments, the filter 612 may include a first plurality of series BAWresonators and a second plurality of shunt BAW resonators. The filter612 may filter the RF signals received from the ASM 608 and passportions of the RF signals within a predetermined bandpass to thetransceiver 620.

When transmitting outgoing RF signals, the ASM 608 may couple theantenna structure 604 with the PA 616. The PA 616 may receive RF signalsfrom the transceiver 620, amplify the RF signals, and provide the RFsignals to the antenna structure 604 for over-the-air transmission.

The processor 624 may execute a basic operating system program, storedin the memory 628, in order to control the overall operation of thewireless communication device 600. For example, the main processor 624may control the reception of signals and the transmission of signals bytransceiver 620. The main processor 624 may be capable of executingother processes and programs resident in the memory 628 and may movedata into or out of memory 628, as desired by an executing process.

The transceiver 620 may receive outgoing data (e.g., voice data, webdata, e-mail, signaling data, etc.) from the processor 624, may generateRF signals to represent the outgoing data, and provide the RF signals tothe PA 616. Conversely, the transceiver 620 may receive RF signals fromthe filter 612 that represent incoming data. The transceiver 620 mayprocess the RF signals and send incoming signals to the processor 624for further processing.

In various embodiments, the wireless communication device 600 may be,but is not limited to, a mobile telephone, a paging device, a personaldigital assistant, a text-messaging device, a portable computer, adesktop computer, a base station, a subscriber station, an access point,a radar, a satellite communication device, or any other device capableof wirelessly transmitting/receiving RF signals.

Those skilled in the art will recognize that the wireless communicationdevice 600 is given by way of example and that, for simplicity andclarity, only so much of the construction and operation of the wirelesscommunication device 600 as is necessary for an understanding of theembodiments is shown and described. Various embodiments contemplate anysuitable component or combination of components performing any suitabletasks in association with wireless communication device 600, accordingto particular needs. Moreover, it is understood that the wirelesscommunication device 600 should not be construed to limit the types ofdevices in which embodiments may be implemented.

Various example embodiments are described below.

Example 1 may include a bulk acoustic wave (BAW) resonator comprising: aborder region that is located between an inactive region and an activeregion along a first axis; a substrate in the inactive region, borderregion, and active region, the substrate to include silicon (Si); amirror layer coupled with the substrate layer, the mirror layer disposedin the inactive region, border region, and active region and including aplurality of layers of Silicon Oxide (SiO2) and a plurality of layers ofTungsten (W); a bottom electrode layer coupled with the mirror layer,the bottom electrode layer disposed in the border region and the activeregion and including a layer of Tungsten (W) and a layer ofAluminum-Copper (AlCu); a piezoelectric layer coupled with the bottomelectrode layer, the piezoelectric layer disposed in the border regionand the active region and including Aluminum Nitride (AlN); a topelectrode layer coupled with the piezoelectric layer, the top electrodelayer disposed in the border region and the active region and includinga layer of Tungsten (W) and a layer of Aluminum-Copper (AlCu); and aplanarization layer coupled with the mirror layer adjacent to thepiezoelectric layer along the first axis, the planarization layer beingdisposed in the inactive region and including the planarizationmaterial.

Example 2 may include the BAW resonator of example 1, wherein theplanarization material includes Silicon Oxide (SiO2), Silicon Nitride(SiN), or Hafnium Oxide (HfO2).

Example 3 may include the BAW resonator of examples 1 or 2, furthercomprising a mass layer coupled with the top electrode layer in theborder region.

Example 4 may include the BAW resonator of examples 1 or 2, wherein theborder region includes a portion of the piezoelectric layer, topelectrode, bottom electrode layer, or mirror layer with reduced mass.

Example 5 may include a bulk acoustic wave (BAW) resonator comprising: apiezoelectric layer that includes a piezoelectric material and locatedbetween a first electrode and a second electrode in an active region anda border region of the BAW resonator; and a planarization layer thatincludes a planarization material that is different than thepiezoelectric material and is located adjacent to the piezoelectriclayer in an inactive region of the BAW resonator that is adjacent to theborder region of the BAW resonator, the planarization layer to improvesuppression of spurious resonances of the BAW resonator.

Example 6 may include the BAW resonator of example 5, wherein theplanarization material includes Silicon Oxide (SiO2), Silicon Nitride(SiN), or Hafnium Oxide (HfO2).

Example 7 may include the BAW resonator of example 5, wherein thepiezoelectric material includes Aluminum Nitride (AlN).

Example 8 may include the BAW resonator of any of examples 5-7, whereinthe second electrode is a bottom electrode that is coupled with a mirrorlayer.

Example 9 may include the BAW resonator of example 8, wherein the mirrorlayer is a Bragg mirror layer.

Example 10 may include the BAW resonator of example 8, wherein themirror layer includes one or more layers of a conductive material andone or more layers of a dielectric material.

Example 11 may include the BAW resonator of any of examples 5-7, whereinthe border region includes a mass layer coupled with the first electrodein the border region on a side of the first electrode opposite thepiezoelectric layer.

Example 12 may include the BAW resonator of any of examples 5-7, whereinthe border region includes a portion of the piezoelectric layer, firstelectrode, second electrode, or mirror layer.

Example 13 may include the BAW resonator of any of examples 5-7, whereinthe first electrode or the second electrode include an Aluminum-Copper(AlCu) layer and a Tungsten (W) layer.

Example 14 may include a bulk acoustic wave (BAW) resonator comprising:an active region that is coupled with and adjacent to a border regionalong a first axis; an inactive region that is coupled with and adjacentto the border region on a side of the border region opposite the activeregion; a piezoelectric layer located between a top electrode and abottom electrode along a second axis that is perpendicular to the firstaxis in the active region and the border region; a mirror layer coupledwith the piezoelectric layer along the second axis; and a planarizationlayer that is adjacent to and coupled with the piezoelectric layer alongthe first axis in the inactive region.

Example 15 may include the BAW resonator of example 14, wherein themirror layer includes Silicon Oxide (SiO2).

Example 16 may include the BAW resonator of example 14, wherein themirror layer includes one or more layers of Silicon Oxide (SiO2) and oneor more layers of Tungsten (W).

Example 17 may include the BAW resonator of any of examples 14-16,wherein the piezoelectric layer includes Aluminum Nitride (AlN).

Example 18 may include the BAW resonator of any of examples 14-16,wherein the border region includes a mass layer coupled with the topelectrode in the border region on a side of the top electrode oppositethe piezoelectric layer.

Example 19 may include the BAW resonator of any of examples 14-16,wherein the border region includes a portion of the piezoelectric layer,top electrode, bottom electrode, or mirror layer with reduced mass.

Example 20 may include the BAW resonator of any of examples 14-16,wherein the top electrode or the bottom electrode include anAluminum-Copper (AlCu) layer and a Tungsten (W) layer.

Example 21 may include the BAW resonator of any of examples 14-16,wherein the planarization material includes Silicon Oxide (SiO2),Silicon Nitride (SiN), or Hafnium Oxide (HfO2).

Although the present disclosure has been described in terms of theabove-illustrated embodiments, it will be appreciated by those ofordinary skill in the art that a wide variety of alternate and/orequivalent implementations calculated to achieve the same purposes maybe substituted for the specific embodiments shown and described withoutdeparting from the scope of the present disclosure. Those with skill inthe art will readily appreciate that the teachings of the presentdisclosure may be implemented in a wide variety of embodiments. Thisdescription is intended to be regarded as illustrative instead ofrestrictive.

What is claimed is:
 1. A method of fabricating a bulk acoustic wave(BAW) resonator comprising: depositing a substrate layer includingsilicon (Si) in an inactive region, an active region, and a borderregion therebetween, the substrate layer parallel to a first axisintersecting the border region, the inactive region, and the activeregion; depositing a mirror layer including a plurality of layers ofSilicon Oxide (SiO2) and a plurality of layers of Tungsten (W) in theinactive region, border region, and active region such that the mirrorlayer is coupled with the substrate layer; depositing a bottom electrodelayer including a layer of Tungsten (W) and a layer of Aluminum-Copper(AlCu) in the border region and the active region such that the bottomelectrode layer is coupled with the mirror layer; depositing apiezoelectric layer including Aluminum Nitride (AlN) in the borderregion and the active region such that the piezoelectric layer iscoupled with the bottom electrode layer; depositing a top electrodelayer including a layer of Tungsten (W) and a layer of Aluminum-Copper(AlCu) in the border region and the active region such that the topelectrode layer is coupled with the piezoelectric layer and the topelectrode layer; and depositing a planarization layer including aplanarization material in the inactive region such that theplanarization layer is coupled with the mirror layer and adjacent to thepiezoelectric layer, the planarization layer and the piezoelectric layerintersecting the first axis.
 2. The method of claim 1, wherein theplanarization material includes Silicon Oxide (SiO₂), Silicon Nitride(SiN), or Hafnium Oxide (HfO₂).
 3. The method of claim 1, furthercomprising depositing a mass layer such that the mass layer is coupledwith the top electrode layer in the border region.
 4. The method ofclaim 1, wherein the border region includes a portion of thepiezoelectric layer, top electrode, bottom electrode layer, or mirrorlayer with reduced mass.
 5. A method of fabricating a bulk acoustic wave(BAW) resonator comprising: depositing a first electrode; depositing apiezoelectric layer that includes a piezoelectric material in an activeregion and a border region such that the piezoelectric layer is coupledwith the first electrode; depositing a second electrode such that thepiezoelectric layer is vertically located between the first electrodeand the second electrode; and depositing a planarization layerhorizontally adjacent to the piezoelectric layer in an inactive regionthat is horizontally adjacent to the border region, the planarizationlayer including a planarization material that is different than thepiezoelectric material.
 6. The method of claim 5, wherein theplanarization material includes Silicon Oxide (SiO₂), Silicon Nitride(SiN), or Hafnium Oxide (HfO₂).
 7. The method of claim 5, wherein thepiezoelectric material includes Aluminum Nitride (AlN).
 8. The method ofclaim 5, further comprising depositing a mirror layer; whereindepositing a second electrode comprises depositing a bottom electrodesuch that the mirror layer is coupled with the bottom electrode.
 9. Themethod of claim 8, wherein the mirror layer is a Bragg mirror layer. 10.The method of claim 8, wherein the mirror layer includes one or morelayers of a conductive material and one or more layers of a dielectricmaterial.
 11. The method of claim 5, further comprising depositing amass layer in the border region such that the mass layer is coupled withthe first electrode in the border region on a side of the firstelectrode opposite the piezoelectric layer.
 12. The method of claim 5,wherein the border region includes a portion of the piezoelectric layer,first electrode, second electrode, or mirror layer.
 13. The method ofclaim 5, wherein the first electrode or the second electrode include anAluminum-Copper (AlCu) layer and a Tungsten (W) layer.
 14. A method offabricating a bulk acoustic wave (BAW) resonator comprising: depositinga mirror layer in an inactive region, an active region, and a borderregion, the active region coupled with and adjacent to the borderregion, the inactive region coupled with and adjacent to the borderregion on a side of the border region opposite the active region, theactive region and the border region intersecting a first axis, themirror layer perpendicular to and intersecting a second axis that isperpendicular to the first axis; depositing a bottom electrode thatintersects the second axis; depositing a piezoelectric layer thatintersects the first axis and the second axis such that the mirror layeris coupled with the piezoelectric layer; depositing a top electrode thatintersects the second axis such that the piezoelectric layer is locatedbetween the top electrode and the bottom electrode; and depositing aplanarization layer that intersects the first axis in the inactiveregion such that the planarization layer is adjacent to and coupled withthe piezoelectric layer.
 15. The method of claim 14, wherein the mirrorlayer includes Silicon Oxide (SiO₂).
 16. The method of claim 14, whereinthe mirror layer includes one or more layers of Silicon Oxide (SiO₂) andone or more layers of Tungsten (W).
 17. The method of claim 14, whereinthe piezoelectric layer includes Aluminum Nitride (AlN).
 18. The methodof claim 14, further comprising depositing a mass layer such that themass layer is coupled with the top electrode layer in the border regionon a side of the top electrode opposite the piezoelectric layer.
 19. Themethod of claim 14, wherein the border region includes a portion of thepiezoelectric layer, top electrode, bottom electrode, or mirror layerwith reduced mass.
 20. The method of claim 14, wherein the top electrodeor the bottom electrode include an Aluminum-Copper (AlCu) layer and aTungsten (W) layer.
 21. The method of claim 14, wherein theplanarization material includes Silicon Oxide (SiO₂), Silicon Nitride(SiN), or Hafnium Oxide (HfO₂).